Underwater transducer having a longitudinally vibratile element



Nov. 22, 1960 L. w. CAMP 2,961,637

UNDERWATER TRANSDUCER HAVING A LONGITUDINALLY VIBRATILE ELEMENT FiledJune 24, 1955 I3 I3 /7 139' I9 1/ Acousr/c INSULATING/0 l0 [5 i IMATERIAL I 25 25 3/ a l\\\ t L [3- i\\\\\\\\\\'.\\\\\\\\\\ I3 I mmvrox27 Leon W Camp ATTORNEY UNDERWATER TRANSDUCER HAVING A LONGI- TUDINALLYVIBRATILE ELEMENT Leon W. Camp, Glendale, Califl, assignor to The BendixCorporation, a corporation of Delaware Filed June 24, 1955, Ser. No.517,814

13 Claims. (Cl. 340-) This invention relates to underwater transducersfor converting electrical oscillations into traveling pressure waves inliquids, and vice versa, and is particularly applicable to transducersutilzing as the active element or elements longitudinally vibratileelectromechanically-responsive elements.

Underwater transducers usually consist of a watertight casing containingone or more vibratile elements so arranged as to have one faceacoustically coupled to the surrounding water and the remaining surfaceacoustically insulated from the Water (and from the other vibratileelements when there are more than one). Air or other gas is an excellentinsulating medium, but it is most commonly utilized as a filling in thepores of porous yieldable material, such as cellular rubber, cork, etc.,which materials provide some mechanical support and lock the air againstdisplacement by liquid in which the vibratile elements may be immersed.To provide acoustic conduction between the working faces of thevibratile elements and the exterior water, it has also been commonpractice to provide a rubber sound window in the casing and fill thecasing with a sound-conducting insulating liquid. When such transducersare submerged to substantial depths or otherwise exposed to high staticpressure, the pressure is applied to the liquid filling the casing tocompress the sound-insulating cellular material, thereby introducingsevere problems of design.

In accordance with the present invention, the necessity of a soundwindow is eliminated, and an unobstructed air space is substituted forat least a part of the usual cellular insulating material. This isacocmplished by exposing the working faces of the vibratile elementsdireotly to the waetr and sealing the sides of the elements to thecasing against ingress of water with rubber O-rings, which have longbeen used as sealing rings on pistons and the like in hydraulicapparatus. The O-rings not only seal the air spaces about the elementsunder high hydrostatic pressure, but yieldably support the elements forvibration with respect to the casing.

An object of the invention is to provide an effective and practicalconstruction for transducers subject to high static pressures such asexist at substantial depths in water.

Another object is to provide a transducer unit that is well insulatedacoustically at the sides and is adapted for use in combination withother similar units in a large array to obtain desired directivepatterns.

Other more specific objects and features of the invention and theadvantages of the invention will be apparent from the following detaileddescription with reference to the drawing, in which:

Fig. 1 is a front end view of a multi-unit transducer incorporating theinvention.

Fig. 2 is a side elevation of the same transducer.

Fig. 3 is a longitudinal section showing details of one of the units ofthe transducer of Figs. 1 and 2.

Fig. 3a is an enlarged portion of Fig. 3.

Fig. 4 is a longitudinal section similar to Fig. 3, but showing analternative construction.

2,961,637 Patented Nov. 22, 1950 passages containing separate vibratileelements 13 (Fig.-

3) associated with'the respective heads 13a. The body 10 may be of arigid material, but it is conveniently cast or molded from a stillplastic material, such as Epoxy-elastomer mixture, with sleeves 15 ofmore rigid material, such as metal, defining the cylindrical passages.

Referring to Fig. 3, each vibratile element 13 comprises one of theheads 13a, a hollow cylindrical body 13b of electromechanicallysensitive material, such as barium titanate, having electrodes 13cbonded to its ends, and a rear head 13d. The heads 13a and 13d arepreferably of metal, the front head being of a metal that is relativelyresistant to corrosion by water. Titanium has been found to be anexcellent metal for this purpose. The heads are firmly bonded to theopposite ends of the vibratile body 13b with an insulating bondingmaterial 13e. Glass has been found to be excellent for this purpose. Inmanufacture, a disk of glass is placed between each end of the body 13band the adjacent heads 13a and 13d, and the assembly is placed in afurnace and heated to a temperature suflicient to fuse the glass. Theelectrodes 13c are the conventional silver coatings which themselves arevery tightly bonded to the body 13. In turn, the glass 132 forms a tightbond between the electrodes and the heads 13a and 13d, respectively. Itis desirable to form the body 13b of slightly smaller diameter than theheads 13a and 13d and recess the heads to receive the body, as shown inFig. 3. The glass may flow into the narrow clearance space between thesides of the recesses in the heads and the sides of the body 13b, asshown in Fig. 3a (in which the clearance space is exaggerated).

Each of the heads 13a and 13d is provided with a peripheral groove 17containing a rubber O-ring 18.

The expression O-ring, as used in this specification, including theclaims, has a specific meaning that it has acquired in the hydraulicart. It means a ring of rubber or other elastomer mounted in a groove inone of two cylindrical surfaces to be sealed with respect to each other,and of such dimensions that it does not completely fill the groove butbears lightly against the opposed cylindrical surface in the absence offluid pressure. Fluid pressure on either side of the ring presses itaxially against the opposite side of the groove and expands it radiallyto seal against the bottom of the groove and the opposed cylindricalsurface with a force proportional to the fluid pressure. An essentialcharacteristic of O-rings that distinguishes them from conventionalmechanically compressed rubber gaskets is that they are only lightlydistorted and offer little friction in the absence of pressure, but areincreasingly distorted in proportion to applied pressure only to theextent necessary to maintain the fluid seal.

The two O-rings form a resilient support that maintains the vibratileelement 13 out of contact with the wall of the sleeve 15 but offerslittle impedance to longitudinal vibration of the element 13. Inaddition, the front ring 18 forms a fluid-tight seal to prevent theentry of water through the front end into the space between the element13 and the liner 15. Therefore, this space remains filled with air,which offers excellent acoustic insulation against the transmission ofsound to and from the sides of the vibratile element 13.

As shown in Fig. 3, the vibratile element 13 is shorter than the liner15, and the rear end of the latter is filled with a cylindrical block 19of acoustic insulating material that is relatively dense, so that itdoes not compress excessively in response to large forces impartedthereto by the element 13 in response to high hydrostatic pressuresactingon the front head 13a.v

The rear closure member-.ll'is bonded to the body in fluid-tightrelation so. that it. effectively prevents any entry of water into therear ends of the sleeves 15. The closure member 11 in turn is bonded tothe bracket 12 which may have a face of corresponding size against whichthe rear face of the closure member 11 fits.

To make electricalconnections to the electrodes 13c, the silveredsurfaces constituting said electrodes are extended slightly over theinner edge of the annular body 13b and soldered to Wires 20which extendthrough an aperture provided therefor. in the member 13d and in themember'19. The rear closure member 11 has apertures extending from thefrontface thereof to the rear face thereof opposite each of the elements13 and may have grooves in its rear face for bringing the wires tocommon connector leads 22 which are extended through anaperture'providedfor that purpose in the bracket 12.

As the apparatus is; lowered to substantial depth in water, thehydrostatic force acting on the heads 13a slides the elements 13rearwardly in the liners 15, compressing thesupporting blocks 19 in sodoing. However, as the blocks 19 compress, their resistance to furthercompression increases until an equilibrium is reached. These blocks 19are sufiiciently elastic that they do not seriously dampen thelongitudinal vibratory motion of the element 13.

Fig. 4-shows a simpler version of the invention in which the-vibratileelement 13' consists of a single solid cylinder of electromech anicallysensitive material, such as barium titanate, having the usual silveredelectrodes 22 and 23 on-its opposite ends. In this instance, the grooves24 for the-O-rings 25 are formed directly in the element 13. At itsfront end, the liner may'have a re-entrant lip 26 for limiting forwardmovement of the element 13 with respectto theliner 15'. To makeelectrical connection tothe front electrode *22, it is connected byaflexible lead 27 to the adjacent end of the liner 15'. The rearelectrode 23 is insulated from the liner 15' and is connected. to anungrounded lead 28.

To support the-element 13' against movement in response -to-hydrostaticpressure on its face, it is supported by a glass disk 30 which restsagainst the rear electrode 23 of the element 13' and engages at its edgea split ring 30a which is held in an annular groove 31 in the innersurface of the liner 15. This leaves an air space between the majorportion of the-rear'end of the vibratile element 13 and the rear closuremember 11.

Although for the purpose of explaining the invention a part'cularembodiment thereof has been shown and described, obvious'modificationswill occur to a person skilled in the art, and I do not desire to belimited to the exact details shown and described.

I claim:

1. A transducer comprising; aibody member having a frontend and a rearend and apassage having a cylindrical wall extending therethrough fromone end to the other; a longitudinally vibratoryelectromechanicallysensitive piston element having a cylindrical wallloosely fitting in the passage and one of said walls having annulargrooves adjacent each end; an elastomer O-ring in each annular grooveradially compressed against the juxtaposed wall for resilientlysupporting said piston element out of contact with the wall of saidpassage for longitudinal vibration and eifecting a liquid seal betweensaid piston'element and said passage wall; said piston element having anexposed rigid working face adjacent the front e d of a d bo y, and arear f e; and means bearing 4;. against said rear face of said pistonelement supporting said'piston element against static fluid pressureforces on the face thereof.

2. A transducer according to claim 1 in which said rear face of saidpiston element is positioned within said passage, and saidlast-mentioned means comprises: a cylindrical body of acousticinsulating material extending from said rear face of said pistonto therear end ofsaid body member, and a rear wallmember overlying the rearend of the body member and said body of insulating material.

3. A transducer according toclaim 2 in which said rear wall member is ofsemi-rigid acoustic insulating material bondedto said body member.

4. Apparatus according to claim 1 in which said body member comprises abody of semi-rigid insulating material and a rigid cylindrical shellimbedded therein defining said cylindrical passage.

5. Apparatus according to claim 1 including a plurality of passagesinsaid body and a plurality of piston elements corresponding to andarranged side by side with respect to each other and said mentionedpassage and piston element.

6. A transducer according to claim 1 in which said I one of said headsis of electrically conductive material and is bonded to its adjacentelectrode with an electrical insulating'material.

9. Apparatus according to claim 8 in which said annular grooves are insaid heads.

10. Apparatus according to claim 8 in which said cylindrical body andrear head are hollow, and electrical connection meansextendingtherethrough to said front electrode.

11. In anunderwater transducer: an electromechanically-responsive hollowcylindrical element having flat parallel'rear and'front ends; rear andfront heads bonded to the respective ends of said element andconstituting withsaid element an integral unit vibratile longitudinallyby expansion and contraction, said front head being solid; housing-meansenclosing at least the side and rear portions of said integral un t forpreventing ingress of water thereto; and a body of acoustic insulatingmaterial be tween-said rear head and said housing supporting said unitagainst rearward displacement relative to the housing. 12. Apparatusaccording to claim 11 in which said rear head'is-ahollow cylinder.

13. .Apparatus according to claim 12 in which said rear head and saidhollow cylindrical element have flush internal cylindrical surfaces.

References Cited in the file of this patent UNITED STATES PATENTS1,401,024 Wood et al. Dec. 20, 1921 2,405,472 Tuttle Aug. 6, 19462,497,901 Mott Feb, 21, 1950 2,741,754 Miller Apr. 10, 1956 2,748,369Smyth May 29, 1956

